The present invention is directed to a device for fastening a gripper bar onto a continuous chain train in a machine that processes plate-like workpieces, such as sheets of paperboard or cardboard, as well as to the gripper bar specifically adapted to this device.
A machine for processing paperboard or cardboard usually includes an infeed station in which a pile of sheets is arranged, with every sheet being successively taken from the top of the pile in order to be carried onto a feeding table. On the table, every sheet is positioned against front lays and side-marks before a front edge of the sheet is seized by a series of grippers mounted along a crosswise bar, whose ends are fastened onto a train of lateral continuous chains, which carry the bar and also the sheet into the next processing station sequentially. These processing stations can include a die-cutting press, which is then followed by a waste stripping station. These processing stations are followed by a delivery station in which each sheet is released by the grippers and is aligned prior to being dropped onto a top of an outlet pile of processed sheets.
The device for fastening the gripper bars onto the two trains of lateral chains, which form a continuous loop extending between a driving chain wheel and a driven chain wheel, has to be very solid in order to transmit to the bars and, hence, to the sheets the acceleration and deceleration forces which appear in the course of the intermittent run at high speed throughout the successive stations.
This fastening device also must remain rigid to rotation around an axle which is passed by the chain train in order to limit, as much as possible, the flexing or bending of the bar due to the centrifugal forces occurring during the movement of the chain, particularly when passing around the driving and driven chain wheels, which are arranged on the path of the chain.
In addition, the crossbars which support the grippers are usually made out of hollow profiled pieces in order to remain rigid to flexing and to have minimum weight and, hence, a minimum inertia.
A known fastening device includes a monobloc piece comprising a first part which is an integral part of the chain in which the part replaces one of the links and a second part which lengthens the inner face of the first part and is inserted in the profiled piece of the bar where it is mounted, for instance, with bolts. The length of this monobloc piece, in the direction of the bar, makes it remain rigid to centrifugal forces.
However, the conception of this known fastening device, which comprises a part inserted in the profiled piece, makes it impossible to dismantle the gripper bar for fixing or replacing without having to open the chain train. The opening of the chain train is a particularly difficult and fastidious operation.
In addition, the fastening device is different depending whether it is designed for the left-hand side chain, which is the operator's side, or for the right-hand side chain, which is opposite to the operator, due to the existence of a notch or other orifice for the setting of the first gripper. This fact compels the maintenance of double stocks of spare parts that are symmetrical between them.